Postal Code

A postal code is a sequence of numbers, letters, or both assigned to a specific geographic area to help sort and deliver mail. In the United States, postal codes are called ZIP codes and consist of five digits, sometimes extended to nine with a hyphen (ZIP+4). Postal codes are assigned and maintained by national postal authorities. In the U.S., that's the United States Postal Service (USPS).

How a postal code works

When mail is processed, automated sorting equipment reads the postal code and routes the item to the correct regional facility, then to the appropriate local carrier for final delivery.

The five-digit ZIP code, introduced in 1963, identifies a delivery area such as a city, town, or section of a large city. The first digit represents a broad national region; each subsequent digit narrows the scope to a specific post office or delivery zone. The ZIP+4 extension pinpoints a specific block, building, or P.O. box within that area, reducing sorting errors for high-volume mailers.

Key characteristics

Postal codes follow a defined format and are not self-assigned. A single ZIP code can cover a few city blocks or an entire rural county, and ZIP codes do not align with political or administrative boundaries. Large institutions with high mail volume, such as universities or federal agencies, may have a unique ZIP code.

ZIP code boundaries are not static. The USPS periodically updates them as populations shift and delivery routes change, so businesses should verify their address information remains current.

Why a postal code matters

An incorrect or missing postal code can cause mail to be delayed, misrouted, or returned to sender as undeliverable, which can be a serious problem when the correspondence involves legal notices, tax documents, or business contracts.

For businesses, postal codes carry additional significance. They appear in business registration filings, determine tax jurisdictions, and establish a business' location in public records. Sales tax obligations, for example, can vary across thousands of U.S. jurisdictions based on the ZIP code associated with a transaction or business location, which connects to the concept of business nexus.

Common uses

• Business formation filings: The registered address, including postal code, must be accurately listed on state formation documents.
• Registered agent addresses: A registered office must have a valid street address with a postal code in the state of registration. P.O. boxes are generally not accepted.
• Legal notices: Legal notices and service of process are delivered to the address of record. An incorrect postal code can result in missed correspondence.
• Business licenses and permits: Applications for a business license or business permit require a complete address to determine the applicable jurisdiction.

Postal code vs. ZIP code

In the U.S., the terms are used interchangeably, but ZIP code is a trademarked designation specific to the USPS, while "postal code" is the internationally recognized term. Canada uses alphanumeric postal codes; the United Kingdom uses postcodes. On international forms, "postal code" is the standard field label.

Related terms

• Registered office: The official address where a business receives legal correspondence and service of process.
• Business license: Licensing applications require a complete address with a valid postal code to determine jurisdiction.
• Business nexus: A business' location, identified in part by its postal code, can determine tax and regulatory obligations.

FAQs about postal code

How do I find the correct postal code for a business address?

Use the USPS ZIP Code lookup tool to search by street address, city, and state. The ZIP+4 format is especially useful for business filings, as it identifies a specific building or delivery point.

Can a postal code affect which taxes a business owes?

Yes. The ZIP code associated with a business location or transaction can determine which local tax jurisdictions apply, including sales tax rates and filing obligations. An inaccurate postal code on file with tax authorities can create compliance discrepancies.

When should a business update its postal code with government agencies?

Any time a business relocates, even within the same city, the postal code on file with the IRS, state tax authorities, and the Secretary of State (or equivalent office) should be updated promptly. Failing to do so can result in missed notices and affect the business's standing with those agencies.